The base-field interaction Hamiltonian is given by a dipolar coupling, in the rotating-wave approximation [1]}, [2]}, [3]},
\(H_{BF} = -i\hbar g \sum _\omega (a_\omega \sigma _{a2}^\dagger + b_{\omega } \sigma _{b2}^\dagger - \mbox{H.c.}).\) 
